Fix conda installation in GitHub workflow on macos-14 runner

Fix the following error:

```
Error: No installed conda 'base' environment found at !If you are using this action in a self-hosted runner that already provides its own Miniconda installation, please specify its location with a `CONDA` environment variable. If you want us to download and install Miniconda or Miniforge for you, add `miniconda-version: "latest"` or `miniforge-version: "latest"`, respectively, to the parameters for this action.
```

.github/workflows/osx_startup.yaml

@@ -50,9 +50,10 @@ jobs:
           path: .tox
           key: tox-cache-${{ runner.os }}-${{ steps.full-python-version.outputs.version }}-${{ hashFiles('galaxy root/requirements.txt') }}-osx
       - name: Install miniconda  # use this job to test using Python from a conda environment
-        uses: conda-incubator/setup-miniconda@v2
+        uses: conda-incubator/setup-miniconda@v3
         with:
           activate-environment: ''
+          miniforge-version: latest
       - name: Restore client cache
         uses: actions/cache@v3
         with: